Conventionally, a compact and thin-type image pickup apparatus has come to be mounted on a mobile terminal representing a compact and thin-type electronic device such as a cell phone and PDA (Personal Digital Assistant), whereby, it has become possible to transmit mutually not only voice information but also image information to a remote location.
As an image pickup element used for these image pickup apparatus, a solid-state image pickup element such as CCD (Charge Coupled Device) type image sensor or CMOS (Complementary Metal-Oxide Semiconductor) type image sensor is used.
Recently, following enlargement of the spread of these mobile terminals, a mobile terminal on which an image pickup apparatus employing an image pickup element with high pixel density is mounted in order to take images with high quality is being supplied on the market. This image pickup apparatus sometimes employs an image pickup lens formed of plural lenses in order to enhance the resolution, corresponding to the image pickup element with high pixel density.
As an image pickup lens used for a compact and high-performance image pickup apparatus provided with such an image pickup element with high pixel density, an image pickup lens of four-element structure has been proposed because it can achieve higher performance as compared with an image pickup lens of two- or three-element structure.
As this image pickup lens of four-element structure, there has been disclosed the so-called inverted-Ernostar type image pickup lens which includes, in order from the object side, a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive refractive power, and a fourth lens with positive refractive power with aiming an enhancement of its performance (for example, refer to Patent Literature 1).
Further, there has been discloses the so-called telephoto type image pickup lens which includes, in order from the object side, a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive refractive power, and a fourth lens with negative refractive power with aiming downsizing of the total length of the image pickup lens, which is represented as a distance along the optical axis from the lens surface arranged at the position closest to the object side in the total system of the image pickup lens to a focal point at the image side (for example, refer to Patent Literatures 2 and 3).
Patent Literature 1: JP-A No. 2004-341013
Patent Literature 2: JP-A No. 2002-365529
Patent Literature 3: JP-A No. 2002-365530